Remote control and power system

ABSTRACT

A remote device such as a control value ( 4 ) is powered and controlled by optical energy, supplied by an intensity-modulated light source ( 8 ) and optical fibre ( 10 ). After conversion into electrical form, the light is detected at ( 12 ) and applied to a piezoelectric transformer ( 14 ). The output of the transformer powers and control an actuator ( 16 ) of the control value.

[0001] This invention relates to a system for controlling and providingelectrical power to an electrical device at a remote point. Moreespecially, although not exclusively, the invention concerns a remotemechanical actuation system for remotely controlling and providingelectrical power to a piezoelectric mechanical actuator ormicro-machined electrical system.

[0002] There are many applications where it is required to providemechanical movement remote from a control system such as for example thelaser tracking mechanism in CD players and control flaps on aircraft toname but two. In almost every system the control system transmits anelectrical signal to an electro-mechanical actuator using conductivewires. This electrical signal, which often provides both the electricalpower and control information, is converted into a mechanical moment bythe electro-mechanical actuator which typically comprises an electricmotor, electromagnet, piezoelectric or electrostatic mechanicalactuator.

[0003] Whilst such an arrangement is perfectly adequate for manyapplications it does have inherent limitations associated with theconducting wires making it unsuited for certain applications. Forexample corruption of the electrical signal can arise fromelectromagnetic induction when the wires are run through electricallyand/or magnetically noisy environments. Conversely, when it is requiredto run the wires through electrically and/or magnetically quietenvironments, transmission of the electrical signal can result in theemission of radiation, which can interfere with the operation of otherelectrical systems in the vicinity of the wires. To operate theelectro-mechanical actuator often requires the transmission of highpower electrical signals and this can result in the wires having adiameter which is unacceptable in applications where space and/or weightis of prime concern such as for example in aeronautical applications.Furthermore since the wires are typically made of copper they aretherefore susceptible to failure by fatigue making then unsuited to highvibration environments. Finally in applications where the control systemis a long distance from the actuator, such as for example an oil or gaswell valve which can be located several kilometres from the controlsystem (typically the well head), the length of the connecting wires cangive rise to additional problems. These include limitations on theelectrical signal due to the time constant of the transmission line andresistive loss, both of which decrease the overall system efficiency.

[0004] For high reliability, it is preferred that the electro-mechanicalactuator has no rubbing surfaces such as bearings or pivots, which areprone to wear and for this reason piezoelectric mechanical actuators arefavoured. As is known in order for a piezoelectric actuator to deliverany significant mechanical displacement (e.g. 0.1% strain) this requiresthe application of roughly 1,000 volts per millimetre of thickness ofpiezoelectric ceramic material and they are thus inherently high voltagedevices. Although the required drive voltage can be decreased by usingmultiple thin films of piezoelectric material the reliability of theactuator can be compromised. To avoid the need to transmit high voltagesignals it is known to transmit the electrical signal as a directcurrent signal of a few volts and to convert it to a direct currentelectrical drive signal of between a 100 and 1000 volts usingappropriate circuitry. Typically the circuitry comprises an inverter (dcto ac converter) to convert the direct current signal into analternating current signal, a transformer to step the voltage up to thedesired value and a rectification circuit to convert the signal back toa direct current signal. Such circuitry decreases the overall efficiencyand reliability of the system.

[0005] The present invention has arisen in endeavour to provide a remotemechanical actuation system which in part, at least, overcomes thelimitations of the known systems.

[0006] According to the present invention there is provided a system forcontrolling and providing electrical power to an electrical device at aremote point said system comprising: a light source operable to producean intensity modulated optical signal in response to a control signal,an optical fibre for guiding said optical signal to a photodetectorlocated at said remote point, said photodetector being operable toproduce an electrical signal in response to said optical signal and apiezoelectric transformer connected to said photodetector for convertingsaid electrical signal into a higher voltage second electrical signalfor controlling and providing power to the electrical device.

[0007] Preferably the electrical device comprises a piezoelectricmechanical actuator, micro-machined electrical system or a galliumnitride semiconductor and device.

[0008] Advantageously the light source comprises a solid state laser andthe optical signal is produced by directly modulating the laser usingthe control signal. Alternatively the laser is operable to produce acontinuous optical output and further comprising optical modulationmeans operable to modulate said continuous optical output in response tosaid control signal.

[0009] In order that the invention may be better understood a remotemechanical actuation system in accordance with the invention will now bedescribed by way of example only with reference to the accompanyingdrawing.

[0010] Referring to the drawing there is shown a system 2 for remotelycontrolling and providing electrical power to an aircraft fuel valve 4to regulate the flow of fuel between the fuel tanks and the engine/s.

[0011] The system 2 comprises, in serial connections, a controller 6, asolid state laser 8, an optical fibre 10, a photodetector 12 apiezoelectric transformer 14 and a piezoelectric mechanical actuator 16.The controller 6, which might typically comprise a part of theaircraft's control system, is operable to produce a varying (typicallyup to 100 kHz) direct current electrical control signal, which as willbe described, is used to control and provide electrical power to operatethe piezoelectric mechanical actuator 16 which is mechanically coupledto the fuel valve 4. The electrical control signal is used to drive thelaser 8 such as to produce an intensity modulated optical signal whoseintensity is proportional to the magnitude of the control signal. In theembodiment described the solid state laser is a 980 nm device andproduces an optical output of up to 5W. The output of the laser 8 iscoupled into the optical fibre 10, which can be mono-mode or multi-mode,and the optical signal guided by the fibre 10 to the photodetector 12which converts the optical signal back into a second varying directcurrent electrical signal.

[0012] Typically the photodetector 12 is an array of photodiodes and thesecond signal has a magnitude of between 3 and 6 volts.

[0013] The second electrical signal is applied to the primary of thepiezoelectric transformer 14 which transforms the signal into a highvoltage, typically 300-600V, varying direct current signal which is usedto directly drive the piezoelectric actuator 16. As is known apiezoelectric transformer generally comprises an elongate bar ofpiezoelectric material, often a ceramic of lead zirconate titanate(PZT), having primary and secondary regions. In operation a varyingdirect current electrical signal applied to the primary region excitesvibrations therein which are mechanically coupled to the secondaryregion to induce mechanical stress in the region which are in convertedback into a varying direct current electrical signal of a differentvoltage. The voltage multiplication factor of the transformer isdetermined by the aspect ratio of the output electrode on the secondaryregion. For the embodiment described, which utilises a bulkpiezoelectric actuator rather than a thin film device, themultiplication factor of the transformer is typically more than onehundred times. Unlike a conventional (magnetic) transformer apiezoelectric transformer can directly transform a varying directcurrent signal into a different voltage varying direct current signalwithout the need for inversion and rectification.

[0014] It will be appreciated that the optically controlled remotemechanical actuation system described has a number of advantages overthe known arrangements. Firstly since the control signal is transmittedto the actuator in the form of an optical signal rather than anelectrical signal this makes the system intrinsically safe for use inhigh risk environments and is further immune to interference fromexternal electrical and magnetic fields. For example in the embodimentdescribed the fuel valve 4 will be in close proximity to, or possiblylocated inside, the aircraft's fuel tank and it is probable that thecontrol lines (optical fibres) will have to be routed through the fueltanks which are usually distributed throughout the wings. Consequentlythere is a high risk of explosion should the mechanical actuation systemfail or produce sparks. A further advantage of using an optical fibrerather than conducting wires is that they are extremely small andmechanically very robust making them ideally suited to aeronautic orother applications where mass is of prime concern.

[0015] Further the use of piezoelectric transformer to directly drivethe piezoelectric mechanical actuator offers a number of advantages.Firstly it eliminates the need for the electronic circuitry, inverterand rectifier, normally required when using a conventional magnetictransformer thereby further reducing the system volume and mass.Secondly Piezoelectric transformers are particularly effective wherehigh (>100) voltage multiplication ratios are required as is the casewhen it is desired to drive a piezoelectric actuator from a low voltagecontrol signal. Additionally they are physically smaller than anequivalent conventional wound transformer and their higher efficiency ispreserved irrespective of size and drive frequency. In contrast aconventional magnetic transformer functions less efficiently as the sizedecreases and frequency increases.

[0016] A particular advantage of the system of the present invention isthe system's inherent linearity. As it will be appreciated thedisplacement produced by the actuator is proportional to the magnitudeof the high voltage drive signal which in turn is proportional to theintensity of the optical control signal and the magnitude of theoriginal control signal.

[0017] It will be appreciated that the system of the present applicationis not restricted to the specific application described and canaccordingly be applied to other applications. In a second example it isenvisaged to use the system to control the valves used to regulate theflow of oil and/or gas from wells. After drilling the access hole, thesevalves are inserted into the pipe where they remain in situ for the lifeof the oil field, typically 15 years. The temperature of the field cantypically be 200° C. and the valve can easily be 20 km or more below thewell head. Since an optical fibre typically has a loss of a few tenthsof a decibel per kilometre it is practical in such an application totransmit the control and electrical power in the form of an opticalsignal. Furthermore the piezoelectric transformer and actuator providethe advantage that both are capable of reliable operation up to theircurie temperature (up to 400° C.). Typically the photo detector iscapable of operation up to 250° C. In contrast the typical welltemperatures exceed the upper limit for wound transformers and theassociated drive circuitry (even military grade electronic componentsare usually only rated to 150° C.).

[0018] It will be appreciated that modifications can be made to thesystem described which are within the scope of the invention. Whilst itis convenient to generate the optical signal by directly driving thelaser using the control signal it is envisaged in an alternative systemto generate the optical signal by operating the laser continuously andmodulating its output using an optical modulator or chopper. Furthermoreit will be appreciated that since the spectral purity of the opticalsignal is not critical any light source could be used to generate themodulated optical signal.

[0019] Whilst the use of a piezoelectric transformer and actuatorcombination is particularly preferred, the use of a piezoelectrictransformer in this way to enable the efficient transmission of bothcontrol information and electric power to an electrical device locatedat a remote point is considered to be inventive in its own right.Accordingly in other embodiments the system can be used to control andprovide electrical power to other forms of actuators or devices whichrequire a high drive voltage such as micro-machined electrical systems(MMS) or a gallium nitride semiconductor device which requires a voltagesupply of 100V.

1. A system for controlling and providing electrical power to anelectrical device at a remote point comprising: a light source-operableto produce an intensity modulated optical signal in response to acontrol signal, an optical fibre for guiding said optical signal to aphotodetector located at said remote point, said photodetector beingoperable to produce an electrical signal in response to said opticalsignal and a piezoelectric transformer connected to said photodetectorfor converting said electrical signal into a higher voltage secondelectrical signal for controlling and providing power to the electricaldevice.
 2. A system according to claim 1 in which the electrical devicecomprises a piezoelectric mechanical actuator.
 3. A system according toclaim 1 in which the electrical device comprises a micro-machinedelectrical system.
 4. A system according to claim 1 in which theelectrical device comprises a gallium nitride semiconductor device.
 5. Asystem according to any preceding claim in which the light sourcecomprises a solid state laser.
 6. A system according to claim 5 in whichthe optical signal is produced by directly modulating the laser usingthe control signal.
 7. A system according to claim 5 in which the laseris operable to produce a continuous optical output and furthercomprising optical modulation means operable to modulate said continuousoptical output in response to said control signal
 8. A system forcontrolling and providing electrical power to an electrical device at aremote point substantially as hereinbefore described with reference toor substantially as illustrated in the accompanying drawing.